The present invention generally relates to a new family of biodegradable, environmentally friendly poly(amino acid) polymers and copolymers, as well as, to new and improved methods for making them. More particularly, it relates to high molecular weight poly(amino acid) polymers and copolymer derivatives thereof useful in water treatment applications as coolants and the like. The copolymers are derivatized to incorporate pendant hydroxyl, other, hydroxyalkoxyalkyl, hydroxyalkylaminoalkyl, carboxylate and phosphonate functionality.
Poly(amino acids) are generally known in this art. Polyaspartic acid is known to be biodegradable. However, some modified poly(amino acids) are not biodegradable. For example, a homopolymer of hydroxyethylaspartamide synthesized by reacting a polysuccinimide of aspartic acid with more than 100 mol % of 2-hydroxyethylamine is reported to not be enzymatically degradable. A crosslinked polyhydroxyethylglutamide prepared by reacting poly(L-2-hydroxyethylglutamide) with various amounts of a diaminododecane crosslinking agent is enzymatically degradable, with the rate of degradation increasing with increasing crosslinking density. However, the same linear non-crosslinked polymer is not enzymatically degradable in vivo or in vitro.
The biodegradability and chelating properties of partially derivatized polyaspartic acid have heretofore been unknown and no known method for predicting them have existed prior to this invention. The partially derivatized polyaspartic acid, i.e., aspartic acid containing copolymers, in accordance with this invention were unexpectedly discovered to be more biodegradable and much better scale inhibitors and corrosion inhibitors than both unmodified polyaspartic acid and 100% derivatized polyaspartic acid.
Methods for making poly(amino acid) polymers and copolymers are generally known. Polyaspartic acid is prepared by reacting maleic anhydride with ammonia. Alternatively, maleic anhydride may be reacted with alcohols to form a half ester, and thereafter, reacted with ammonia alone or in combination with amines. These methods are generally effective to prepare rather low molecular weight polymers of less than about 1000. Solid phase polymerization of aspartic acid alone or in the presence of acid catalysts has also been performed. Lower molecular weight materials having molecular weights of less than 50,000 are generally provided by theme methods.
Previous efforts to provide sulfonic acid (e.g., taurine or sulfonomethylamine) functionality to aspartic acid polymers have included reacting the starting materials in a toxic, dimethylformamide solvent. The molecular weights of polymers produced in dimethylformamide solvents are generally very low, i.e., less than about 1000. These processes require the steps of removing toxic DMF and recovering product polymer using complicated and expensive procedures. Moreover, the prior art methods result in degradation of the polymer backbone so that the molecular weights of the resulting products are significantly less than the already low molecular weight starting material.